1. Field of the Invention
The present invention relates generally to valves, and, in particular, to a portable apparatus for machining a valve seat.
2. Description of the Prior Art
A valve seat provides the surface upon which a valve rests to regulate the flow of fluids in piping systems. As such, valve seats are a very important component of a valve system, because failure or erosion of a valve seat results in leakage of the fluid being conveyed. In applications such as power plants, a solid metal valve seat is required because of the extreme pressures and temperatures of the steam, oil, and gases being conveyed. However, even metal valve seats become worn over time, resulting in seepage or leakage.
Valve leakage also results because of the repeated pressure of the valve disk on the seat. As a result, the shape of the valve seat tends to become flattened. Deterioration of the valve seat also occurs because of corrosion, steam and water. In addition, deposits may build up on the valve seat, preventing a tight seal with the disk.
In some applications, replaceable valve seat rings may be utilized, but these types of valve seats also tend to erode and deteriorate. In addition, replaceable seat rings are specially manufactured for only a limited number of valve designs and are simply unavailable for a great many applications.
Therefore, it is typically necessary to replace the entire valve when the valve seat wears away and causes leakage problems. Replacing the entire valve body and interior valve assembly is expensive, time-consuming, and inconvenient. Typically, the valve body is connected with the pipeline by means of welding, and the welds must be taken out in order to remove the valve assembly. Rewelding must then be performed in order to install the new valve assembly, a process which is labor-intensive and expensive.
As an alternative to complete replacement of the valve assembly, it is possible to repair the valve seat by rewelding the seat and machining it to the desired shape, or to simply remachine the valve without welding it first. However, the machining process cannot be accomplished in-line with conventional tools; it is necessary to take out the welds which interconnect the pipe and valve body, lift the valve body out of the line, and transport the valve to and from the machine shop or original equipment manufacturer. This process is very time-consuming and results in substantial shut-down time.
The present invention addresses these and many other problems associated with currently available methods and apparatus for replacing and repairing valve seats.